ECB president says that ‘time and again, the critics of our decisions have been proved wrong’

FRANKFURT—European Central Bank President Mario Draghi launched a robust defense of the ECB’s stimulus in front of an audience of top German financial executives, four days after signaling that the central bank is preparing to expand the program.

Speaking at a reception at German stock-exchange group Deutsche Börse AG, Mr. Draghi squarely addressed his critics in Germany and elsewhere who have warned that a long period of ultralow interest rates creates risks for the economy.